“Writing long books is a laborious and impoverishing act of foolishness: expanding in five hundred pages an idea that could be perfectly explained in a few minutes. A better procedure is to pretend that those books already exist and to offer a summary, a commentary.”

Preface; Variant translations:
It is a laborious madness and an impoverishing one, the madness of composing vast books — setting out in five hundred pages an idea that can be perfectly related orally in five minutes. The better way to go about it is to pretend that those books already exist, and offer a summary, a commentary on them... A more reasonable, more inept, and more lazy man, I have chosen to write notes on imaginary books.
The composition of vast books is a laborious and impoverishing extravagance. To go on for five hundred pages developing an idea whose perfect oral exposition is possible in a few minutes! A better course of procedure is to pretend that these books already exist, and then to offer a resume, a commentary . . . More reasonable, more inept, more indolent, I have preferred to write notes upon imaginary books.
The Garden of Forking Paths (1942)